Abstracts

Rationale: The birth of new neurons or neurogenesis is sustained throughout life in the mammalian brain including humans and is changed by acute seizures. Status epilepticus (SE) transiently enhances neurogenesis; however, patients with chronic epilepsy suffer from learning and cognitive impairments which are associated with a decline in neurogenesis. Kainate is used to model temporal lobe epilepsy and hippocampal damage. Kainate-induced seizures and SE alter hippocampal neurogenesis and coincide with cognitive impairment and mood disorders. Kainate also induces the abnormal formation of new neurons which starts immediately after the insult and is long lasting. However, the mechanisms underlying the birth and the role of the new precursor cells are not fully understood. To gain further insight into the underlying control mechanisms of neural precursors immediately after SE, we examined the acute effects of kainate on hippocampal precursor cells in vitro and on proliferating and quiescent clones of hippocampal precursors in vivo. Methods: Cultured hippocampal cells were prepared from rats P7-10 and exposed to 5µM kainate. BrdU and Ki-67 were used to measure cell proliferation while MitoTrackers, caspase-3 and time-lapse microscopy were used to study cell survival. Nestin and GFAP were used to label radial glial precursors. TuJ1 and doublecortin were used to mark immature neurons and caspase-3 was employed to study cell death. To investigate the effects of kainate in-vivo, clones of proliferating cells in the dentate gyrus were pre-labelled with BrdU 24 hours before kainate injections and examined 6-72 h after the injections. Results: In-vitro, we found that kainate increased the proliferation of radial glial stem cells (nestin and GFAP positive cells that showed inter-kinetic nuclear cell migration under time-lapse videos), via AMPA receptor stimulation. In contrast, kainate decreased progenitor cells (nestin only positive cells). It also enhanced the survival of radial glial precursors and TuJ1 positive cells. Consistently, kainate/seizures in-vivo increased cell proliferation of both proliferating and formerly quiescent radial glial clones of precursors in the granule cell layer (GCL). There was also a preferential increase in the proliferation of the proliferating clones in addition to an increase in the cell cycle exit, without enhancing cell death. Moreover, kainate/seizures increased neural precursors (doublecortin positive cells) in the GCL. Conclusions: We conclude that kainate/seizure enhances hippocampal radial glial precursor proliferation via AMPA receptors, and that it has a differential effect on the proliferation kinetics and fate choice of precursors in the dentate gyrus. This may suggest targeting AMPA receptors would be a possible new strategy in the treatment of epilepsy.